Family Cephalobidae

                                 Rev 10/14/2024

Classification:

      Chromadorea
       Chromadoria
       Rhabditida
        Tylenchina
         Cephaloboidea

          Cephalobidae Filpijev, 1934

Morphology and Anatomy:

• Stoma distinctly jointed; cheilorhabdion wide, rest of stoma narrower.  
• Lip region with probolae
• Stegostom (pharyngeal collar) long

• Scanning electron micrographs of the lip region of females of Cephalobidae (A) Eucephalobus sp. (B) Pseudacrobeles sp. (C) Zeldia punctata (D) Zeldia sp. (E) Acromoldavicus mojavicus (F) Nothacrobeles borregi (G) Cervidellus doorsselaeri (H) Cervidellus alutus (I) Acrobeles sp. Photograph from Nadler et al., 2006

• Esophagus with cylindrical procorpus, isthmus barely seen, basal bulb with a valve. 
• Female gonad prodelphic, reflexed down body, usually with an additional double flexure towards the end of the ovary. Spermatheca usually offset.
• Vulva far from anus.
• Bursa absent in males.

Mountport et al (2000) point out that the suborder Cephalobina (Rhabditida) is significant to basic research on eukaryotic model organisms, including Caenorhabditis elegans because it includes evolutionary progenitors of both plant- and animal-parasitic taxa (Blaxter et al., 1998). However, the taxon is  taxonomic and phylogenetic characteristics of the taxon are not well studied.

Key to subfamilies:
       1. Only cheilorhabdions wider than other parts of stoma                                         Cephalobinae
       2. Cephalic probolae shorter than labial probolae                                                    Acrobelinae
       3. Cephalic probolae large, paddle-shaped, longer than labial probolae.                   Kirjanoviinae
       4. Cheilo- and protostom wider and  the wall more cuticularized than other parts.     Panagrocephalinae

In general, the Cephalobidae differ from the Panagrolaimidae in that :

• the anterior sections of the stoma are very narrow with only the cheilostom awider than other sections
• the postvulval section of the reflexed ovary usually has double flexures.

Distribution

Species of the family Cephalobidae are mostly terrestrial and bacteria-feeding.  They have worldwide distribution. They occur in tropical and temperate regions as well as in hot and cold arid areas globally, including Antarctica..

Cephalobs are especially diverse and abundant in deserts and many species have been described from warm and dry habitats like the Namib Desert in southern Africa (see, e.g.,  Rashid et al. 1990a, b) and the Mojave Desert in southern California (see, e.g., De Ley et al. 1999; Waceke et al. 2005). Sand dunes  appear to be another suitable habitat for cephalobids (Bostrom and Holovachov, 2014). In fact, Bostrom and Holovachoc (2013) consider the Mojave Desert of southern California, and especially the Kelso Dunes, seem to be an area with a high diversity of cephalobids  and perhaps a hot spot for cephalobid diversity. About ten new species have been described from this area and so far one new genus and five new species  from the Kelso Dunes alone (Boström & Holovachov, 2012 & 2013).

References

Blaxter, M. L., P. De Ley, J. R. Garey, L. X. Liu, P. Scheldman, A. Vierstraete, J. R. Vanfleteren, L. Y. Mackey, M. Dorris, L. M. Frisse, J. T. Vida, and W. K. Thomas. 1998. A molecular evolution framework for the phylum Nematoda. Nature 392:71–75.

Bostrom, S. and Holovachov, O. 2013. Description of one new species of Heterocephalobellus Rashid, Geraert & Sharma, 1985 (Rhabditida, Cephalobidae) from Kelso Dunes, Mojave National Preserve, California, USA and Monte desert, Usno, Argentina. J. Nematol. Morphology and Systemastics 16:161-166

Bostrom, S. and Holovachov, O. 2014. Descriptions of species of Stegelleta Thorne, 1938 (Nematoda, Rhabditida, Cephalobidae) from California, New Zealand and Senegal, and a revision of the genus. European Journal of Taxonomy 87:1-19. DOI: https://doi.org/10.5852/ejt.2014.87

De Ley I.T., De Ley P., Baldwin J.G., Mundo-Ocampo M. & Nadler S.A. 1999. Three new species of Nothacrobeles (Nemata: Cephalobidae) from the Mojave Desert, California. Journal of Nematology 31 (4): 482–497.

Filipjev, I.N. 1934. The classification of the free-living nematodes and their relation to the parasitic nematodes. Smithsonian Miscellaneous Collections 89:1-63 + 8 plates.

Mounport, D., P. Baujard, P. De Ley, M. C. Van de Velde, A. Coomans and J. G. Baldwin. 2000. Ultrastructural variation of cuticular layers in Cephalobinae (Nemata: Rhabditida). J. Nematology 32:13-19.

Nadler, S.A., DeLey, P.,Mundo-Ocampo, M., Smythe, A.B.,Stock, S.P., Bumbarger, D., Adams, B.J., Tandingan De Ley, I., Holovachov, O., Baldwin, J.G. 2006. Phylogeny of Cephalobina (Nematoda): Molecular evidence for recurrent evolution of probolae and incongruence with traditional classifications. Molecular Phylogenetics and Evolution. 40: 696-711.

Rashid F., Heyns J. & Coomans A.1990a. Paracrobeles and Acrobeles species from South West Africa/ Namibia with a description of a new Acrobeles species (Nematoda: Cephalobidae). Phytophylactica 22 (1): 41–49.

Rashid F., Heyns J. & Coomans A.1990b. Species of Seleborca from South West Africa/Namibia (Nematoda: Cephalobidae). Phytophylactica 22 (1): 51–62.

Thorne, G. 1937. A revision of the nematode family Cephalobidae Chitwood and Chitwood, 1934. Proc. Helminth Soc. Wash. 4:1-16.

Waceke J.W., Bumbarger D.J., Mundo-Ocampo M., Subbotin S.A. & Baldwin J.G. 2005. Zeldia spannata sp. n. (Nematoda: Cephalobidae) from the Mojave Desert, California. Journal of Nematode Morphology and Systematics 8 (1): 57–67.

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